Many of the medical care garments and products, protective wear garments, mortuary and veterinary products, and personal care products in use today are partially or wholly constructed of nonwoven materials. Examples of such products include, but are not limited to, medical and health care products such as surgical drapes, gowns and bandages, protective workwear garments such as coveralls and lab coats, and infant, child and adult personal care absorbent products such as diapers, training pants, disposable swimwear, incontinence garments and pads, sanitary napkins, wipes and the like. For these applications nonwoven fibrous webs provide functional, tactile, comfort and aesthetic properties which can approach or even exceed those of traditional woven or knitted cloth materials. Nonwoven materials are also widely utilized as filtration media for both liquid and gas or air filtration applications since they can be formed into a lofty filter mesh of fibers having a low average pore size suitable for trapping particulate matter while still having a low pressure drop across the mesh.
Nonwoven materials are commonly produced from fibers made from thermoplastic polymers. Thermoplastic polymers are useful fiber-forming materials for several reasons. Thermoplastic polymers are readily spun into fibers by such processes well known to the art as staple fiber spinning, spunbonding and meltblowing, and fibers formed from thermoplastic polymers are readily bondable by simple methods such as heat and pressure. Also, certain thermoplastic polymers are elastomers and when formed into fibers produce fibers having properties of stretch and recovery. Additionally, fabrics made from thermoplastic fibers may be bonded and/or thermoformed into shaped articles by the selective application of heat and pressure. However, fibers formed from thermoplastic polymers, and the materials and fabrics formed therefrom, are also subject to damage from excessive heat such as deformation of the nonwoven fabric and may even melt or burn when exposed to heat. Thermoplastic polymers in many cases lack chemical resistance and so may degrade or dissolve in the presence of chemicals.
Thermoset polymers, on the other hand, generally have superior resistance to both chemical degradation and to melting or deforming upon heat exposure. In addition, thermoset polymers when formed into fibers have superior strength, toughness and resilience compared to thermoplastic fibers, and elastic thermoset polymers offer superior stretch and recovery properties compared to thermoplastic elastomers. However, fibers formed from thermoset polymers usually are not bondable by the simple expedient of heat bonding, such as by calender bonding with heat and pressure or through-air bonding with heated air, and a nonwoven web or fabric made entirely from thermoset polymer fibers would therefore require additional bonding media such as adhesives.
Consequently, there remains a need for fibers which have a high level of resilience, strength and toughness and/or high elastic properties, yet are able to be bonded into nonwoven fabrics without the need of additional bonding media such as adhesives. Additionally, there remains a need for a fiber production process for such advantageous fibers which is continuous and can be used in large commercial scale productions.
By varying the types and properties of the thermoset and thermoplastic polymers a nonwoven web can be engineered to maintain certain desired attributes such as thermal bondability while improving various properties such as flame resistance, elasticity, strength, durability, pressure drop and compression-resistant and resilient bulk or loft.